Why do contours on opposite sides of a stream have the same values?

Why do contours on opposite sides of a stream have the same values?

• A. Contours are paired across drains
• B. Contours follow the stream closely
• C. Contours are drawn independently on each side
• D. Contours bend to avoid the stream

Answer: (A)

Contours are lines of equal elevation. In a stream valley, the land on both sides reaches the same height at corresponding points along the valley, so the contour for a given elevation crosses the stream and continues onto the opposite bank. That continuity creates paired contours across the drain. The elevation value is the same on both sides, reflecting a single horizontal plane cutting through the terrain. The other ideas don’t fit because contours aren’t drawn independently on each side, they don’t inherently follow the stream, and they don’t purposely bend to avoid water—they simply trace where that elevation occurs across the landscape.